Process of preparing acrylonitrile and methacrylonitrile by catalytic ammoxidation of propylene and isobutylene



United States Patent 3,426,059 PROCESS OF PREPARING ACRYLONITRILE AND METHACRYLONITRILE BY CATA- LYTIC AMMOXIDATION OF PROPYLENE AND ISOBUTYLENE Jamal S. Eden, Akron, Ohio, assignor to The B. F. Goodrich Company, New York, N.Y., a corporation of New York No Drawing. Filed Aug. 30, 1965, Ser. No. 483,793 US. Cl. 260-4653 12 Claims Int. Cl. C07c 121/04, 121/02 ABSTRACT OF THE DISCLOSURE Propylene or isobutyleue, ammonia and oxygen are contacted at an elevated temperature with a catalyst con taining molybdenum oxide, tellurium oxide and a zinc or cadmium phosphate to form acrylonitrile or methacrylonitrile.

This invention relates to a method of preparing acrylonitrile or methacrylonitrile by ammoxidation of monoolefinic hydrocarbons containing 3 to 4 carbon atoms at an elevated temperature, and relates more particularly to a method of preparing acrylonitrile or methacrylonitrile by passing vapors of propylene or isobutylene, ammonia and an oxygen containing gas at a temperature of from about 375 C. to about 500 C. over a catalyst comprising a mixture of a molybdenum oxide, tellurium oxide and a zinc or cadmium phosphate in a molar ratio of 100 M00 100 TeO and 10-100 of a zinc or cadmium phosphate. The catalyst can also be designated as Mo Te M P O with P being in the form of a phosphate i.e. each P atom is attached to 3 to 4 oxygen atoms.

Nitriles have been prepared by ammoxidation of hydrocarbons, especially from the normally gaseous hydrocarbons. However, prior catalysts and procedures for ammoxidizing propylene or isobutylene to acrylonitrile or methacrylonitrile have certain shortcomings. The catalysts either have a very short active life, or they convert only a portion of the hydrocarbon to the desired unsaturated nitrile per pass; they oxidize the hydrocarbon excessively to form high proportions of carbon monoxide or carbon dioxide or both or they are not sufficiently selective, so that the hydrocarbon molecule is attacked at both the olefinic unsaturation and at a methyl group and large amounts of HCN and acetonitrile are formed.

It is therefore unexpected to find a catalyst that will convert from over 50 to as high as 100% per pass of a monoolefin containing 3 to 4 carbon atoms to yield very high proportions of acrylonitrile or methacrylonitrile. A further unexpected feature is the unusually long active life of the catalyst.

THE REACTANTS The essential reactants are propylene or isobutylene, ammonia and an oxygen containing gas, which can be pure oxygen, oxygen enriched air or air without additional oxygen. For reasons of economy, air is the preferred oxygen containing reactant.

The addition of steam into the reactor along with the monoolefin, ammonia and an oxygen containing gas is desirable but not absolutely essential. The function of steam is not clear, but it does seem to reduce the amount of carbon monoxide and dioxide in the effluent gases.

Other diluent gases can be used. Surprisingly, saturated hydrocarbons such as propane or butane are rather inert under the reaction conditions. Nitrogen, argon, krypton or other known inert gases can be used as diluents if 0 desired but are not preferred because of the added cost. 7

3,426,059 Patented Feb. 4, 1969 THE CATALYST AND ITS PREPARATION There are several methods for the preparation of the catalyst, which can be supported or unsupported. It is possible to dissolve each of the starting ingredients in water and combine them from the aqueous solutions or the ingredients can be dry blended. Because of the more uniform blend obtained by the solution procedure, it is preferred.

A general procedure for preparing a catalyst from water soluble ingredients is to provide the requisite amount of a molybdenum salt, a tellurium salt and a zinc salt in water. Add the requisite amount of phosphoric acid to the zinc salt solution. Add the tellurium salt solution to the molybdenum salt solution and then add the \zinc saltphosphoric acid mixture to the molybdenum-tellurium salt mixture. The catalyst is then dried and baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding an aqueous slurry of the support to the aqueous solution of catalyst or the aqueous catalyst ingredients can be added to the slurry of the support.

Alternately a slurry of the catalyst ingredients can be prepared in water, then dried and baked. For supported catalysts the aqueous slurry of the catalyst ingredients can be added to an aqueous suspension of the support or vice versa, and then dried and baked.

A third method is to blend the dry ingredients and then mix them thoroughly. The main difficulty is to obtain thorough blending and uniform particle size.

A specific procedure for making the catalysts is as follows:

In this procedure the ingredients are precipitated on blending.

(a) Dissolve 105.96 g. of ammonium molybdate in 160 ml. of water.

(b) Dissolve 3 1.922 g. Te0 in concentrated HC1 and filter if necessary.

Add the tellurium salt solution to the ammonium molybdate solution. A precipitate forms.

(0) Dissolve 54.5 g. of ZnCl in 50 ml. of water and add 46.2 g. of H PO Add this mixture slowly to the precipitated ammonium molybdate-TeO mixture. Dry the mixture on a steam bath and bake for 16 hours at 400 C. Thereafter the catalyst is ground to the desired mesh size and sieved. For supported catalysts an aqueous slurry of the support can be added to the catalyst ingredients or vice versa prior to drying and baking.

Among the suitable supports are silica, silica containing material such as diatornaceous earth and kieselguhr, silicon carbide, clay, aluminum oxides and even carbon, although the latter tends to be consumed during the reaction.

If the catalyst is to be supported the aqueous solution of ingredients can be added to an aqueous slurry of the support or vice versa, prior to drying. The procedure after drying is the same as that already described. Thus, to the aqueous catalyst ingredients 240 g. (1.2 mols) of a 30- 35% aqueous colloidal dispersion of microspheroidal silica (Ludox H.S.) are added slowly with stirring. Stirring is continued for about 4 hour prior to drying. Another procedure is to add the mixtures described under (c) to the Ludox and then add the requisite amount of Te0 and M00 as a slurry. Also the ingredients can be added to the Ludox individually if desired.

Another method is to grind M00 TeO and a zinc phosphate to the proper particle size and then thoroughly mix the dry powders. The mixture can be added to an aqueous slurry of a support or vice versa and thereafter dried and baked.

For fixed bed systems a 10-18 mesh (U.S. Sieve) size is satisfactory. For fluid bed systems the catalyst particle size should be 80325 mesh (U.S. Sieve).

The exact chemical structure of the catalysts made by the above procedures is not known, but catalysts with molar ratios of 100 Mo, 10-100 Te and 10-100 of a zinc phosphate can be used for converting the monoolefinic hydrocarbon to a nitrile. The catalyst contains chemically bound oxygen so that the generic formula can be written as M003 1 TeO Zn O O 10 Th6 phosphate can be a P0 radical, pyrophosphate or a polyphosphate of zinc or cadmium.

A preferred catalyst is one having a ratio of about 75 M00 25 TeO and 25 Zn2P207 because it gives a high yield of desired products and the preferred support is below the dew point pressure of the acrylonitrile or methacrylonitrile at the reaction temperature.

The example is intended to illustrate the invention but not to limit it.

EXAMPLE I reactor. Outlet vapors were passed through a short water i' ii g g i ig 1: 5 2F522? g igi g Charac cooled condenser. Uncondensed gases were passed through S y p a gas chromatograph (Perkin-Elmer Model 154D) and Mo Te Zn P analyzed continuously. The liquid condenser was weighed and then analyzed for its acrylonitrile content in the gas REACTION CONDITIONS chromatograph The reaction can be carried out in either a fixed or at a temperature of WaS first Passed fluidized catalyst bed into this fixed bed reactor. Then propylene and air were The reaction temperature can range from about 375 to fed Separately Into the Stream of Water p The miXtllre 500 C. but the preferred range is from abo t 400 to passed through a pro-heater and entered the reactor at a about 430 C. Below about 375 C. the conversion f temperature of 200250 C. The reactor was preheated monoolefin per pass and yield of unsaturated nitrile is to 'f befofe the gas feed Was baglm- T molar lower than desirable. Usually, a longer contact time is ratlo of the feed was 3 1015 of Oxygen PP as needed at lower temperatures to obtain the yields of un- P mol of P py themols f Wa p r mol of propylsaturated nitriles obtainable at temperatures in the optiwe and "1015 of am{n0n1a P mol of Propylene and the mum range. Above 480 C. some of the acrylonitrile ap- 3O temperature are indicated in the table below. The cold pears to be oxidized to carbon oxides, a etonit il d contact time was 39 seconds. No acetonitrile could be de- HCN. This is much more apparent at about 500 C. tected in the effluent gases.

M01 percent M01 percent yield on Run Temp, Mols Mols propyl propylene converted M01 percent efliciency N0. O. NH; H2O converted Aer AA Aen Aer AA Acn 425 0. 86 4. 3e 91. 3 25. is 14.10 36. 21 22. 47 12.87 33. us 450 0. 86 4. 3e 83. 5 14. a. 84 61.20 12. 15 3. 71 51. 10 445 1. 2 3. 9s es. 0 14. 37 2. 42 65. 3s 9. 05 1. 46 41. 19 445 1. 29 3. 95 60. 0 3. 2s 4. 68 75. 82 1. 97 2. s1 45. 50

Acr=Acrolcin. AA=Acry1ic acid. Acn=Acrylonitrile.

The mol ratio of oxygen to propylene should be from 1.5 to 1 and preferably from 2 to 1 to 4 to 1 for good conversion and yields, but ratios with some excess oxygen, 33 to 100% is even more desirable and is preferred. There is no critical upper limit as to the amount of oxygen, but when air is used as the oxygen containing gas it becomes apparent that too great an excess will require large reactors, pumping, compressing and other auxiliary equipment for any given amount of desired end product. It is therefore best to limit the amount of air to provide 33 to 66% excess of oxygen. This range provides the largest proportion of nitrile, under given reaction conditions. Also, since care is needed to avoid an explosive mixture the limiting of air aids in that direction. The mol ratio of ammonia to propylene can range from about 0.5 to 1 to about 1.75 to l. The preferred ratio of 0.75 to 1.5 of ammonia per mol of propylene.

The molar ratio of steam to propylene can range from 0 to about 5 to 7, but best results are obtained with molar ratios of about 3 to 5 per mol of propylene and for this reason are preferred.

The contact time can vary considerably in the range of about 2 to 70 seconds. Best results are obtained in a range of about 8 to 54 seconds and this range is preferred.

The particle size of catalyst for fixed bed and fluid bed systems has already been described.

The reaction can be run at atmospheric pressure, in a partial vacuum or under induced pressure up to 50-100 p.s.i. Atmospheric pressure is preferred for fixed bed systems and a pressure of 1 to 50 p.s.i. for fluid bed reactions. Care is needed to operate at a pressure which is The hydrocarbons which are ammoxidized according to this invention have the formula The desired end products result from the ammoxidation of only one methyl group on the hydrocarbon molecule, while the terminal CHz=C group remains intact.

The nitriles produced can be defined as alpha, beta monoolefinically unsaturated nitriles having 3 to 4 carbon atoms and a terminal CHFC/ group or they can be defined by the general formula comprising, passing a mixture of a molecular oxygen conta1n1ng gas in a quantity suflicient to provide a molar ratio of from about 1.5 to about 4 mols of oxygen per mol of a hydrocarbon of the formula H ((|3H2)0-1 C lia-:011;

one mol of said hydrocarbon, and from about 0.5 to 1.75 mols of ammonia per mol of said hydrocarbon, over a catalyst consisting essentially of a mixture of molybdenum oxide, tellurium oxide and zinc or cadmium phosphate in a molar ratio of 100 molybdenum oxide, l0-100 tellurium oxide and -100 of zinc or cadmium phosphate at a temperature of from about 375 to about 500 C. at a contact time of from about 2 to 70 seconds.

2. The method of claim 1 in which the hydrocarbon is propylene and the temperature ranges from about 400 to about 480 C. to thereby produce acrylonitrile.

3. A method of preparing acrylonitrile comprising passing a mixture containing a molar ratio of one mole of propylene, sufficient molecular oxygen containing gas to provide from about 2 to about 4 mols of oxygen per mol of propylene, from up to about 7 mols of water vapor per mol of propylene and from about 1.25 to about 1.5 mols of ammonia per mol of propylene over a catalyst consisting essentially of a mixture of M00 TeO and a zinc phosphate in a molar ratio of 100 M00 10-100 TeO and 10-100 of zinc phosphate at a temperature of from about 400 to about 480 C. with a contact time of 8 to 54 seconds.

4. The method of claim 3 in which the catalyst has 75 M003, Te0 and 21121 207.

5. A method of preparing acrylonitrile comprising passing a mixture of about 3 mols of oxygen supplied as air, about 4 mols of water vapor and about 1.25-1.3 mols of ammonia per mol of propylene through a bed of a catalyst consisting essentially of M00 TeO and Zn P O, in a molar ratio of about 75 M00 25 TeO and 25 Zn P O at a temperature of about 440 C. and a cold contact time of about 38 seconds.

6. The method of claim 1 in which the catalyst is in a fixed bed.

7. The method claim 1 in which the catalyst is impregnated on a silicic support.

8. A method of preparing methacrylonitrile comprising passing a mixture containing a molar ratio of one mol of isobutylene, a molecular oxygen containing gas in a quantity suflicient to provide from about 2 to about 4 mols of oxygen per mol of isobutylene, up to 5 mols of water vapor and from 1 to 1.75 mols of ammonia per mol of isobutylene, through a catalyst consisting essentially of a mixture of M00 TeO and a zinc phophate in a molar ratio of 100 M00 10-100 TeO and 10-100 of a zinc phosphate at a temperature of from about 400-500 C. and a contact time of from about 2 to about seconds.

9. The method of claim 8 in which the catalyst has a molar ratio of M00 25 Te0 and 25 Zn P O 10. The method of claim 8 in which the temperature is 400-480 C.

11. The method of claim 1 wherein the catalyst contains a major proportion of M00 and lesser proportions of T e0 and a cadmium pyrophosphate.

12. A method of preparing acrylonitrile comprising passing a mixture containing a molar ratio of one mol of propylene, sufiicient molecular oxygen containing gas to provide from about 2 to about 4 mols of oxygen per mol of propylene, from up to about 7 mols of water vapor per mol of propylene and from about 1.25 to about 1.5 mols of ammonia per mol of propylene over a catalyst consisting essentially of a mixture of M00 Te0 and a cadmium phosphate in a molar ratio of M00 10- 100 Te0 and 10-100 of a cadmium phosphate at a temperature of from about 400 to about 480 C. with a contact time of 8 to 54 seconds.

References Cited FOREIGN PATENTS 1,255,121 1/1961 France.

JOSEPH P. BRUST, Primary Examiner.

U.S. Cl. X.R. 

